B.Core B: Summary Core B will consolidate services for all research projects by providing housing, colony management services (including genotyping, breeding, and timed pregnancies), and technical services (ES-blastocyst chimeras, ES-tetraploid chimeras, and pronuclear injections) for all mice used by the three Projects. The Core will purchase and house animals (mice) for all three projects, including all extant mutant and control wild-type mouse strains, as well as wild-type colonies for generation of new mutant mouse lines. On average, the Core's mice will be housed in 260 cages. The Core will be directed by Dr. J. Richard Chaillet, who has 20 years of experience in mouse molecular genetics, including expertise in generating transgenic mice, mutant mouse lines from mutant ES cells, and ES-tetraploid chimeras. The Core will be maintained and operated by two Research Specialists, who together have the necessary technical skills and experience to perform all of the Core's functions. Dr. Chaillet will supervise the Research Specialists on a daily basis, assigning research projects and coordinating efforts with Drs. Barak and Sadovsky to maintain an efficient Core in terms of completing assignments, mouse usage, housing, and sharing of supplies and biological matehals. Many months are required to generate new transgenic and knockout mouse lines from BACs and mutant ES lines, respectively. Because of this, the appropriate technical service will be provided within four weeks of receiving a transgene construct or ES line from a Project. This will ensure timely delivery of transgenic founders and chimeras. The colony management services provided by the Core are (1) purchase of mice from approved vendors; (2) maintenance of an ongoing breeding colony of wild-type mice to be used as oocyte and embryo donors for technical services such as ES-cell chimeras and transgenic lines; (3) genotyping of mice from housed mutant strains using tail clips as source of DNA, and; (4) providing timed pregnancies from wild-type and mutant strains. The specific technical services provided by the Core are (1) generation of ES-blastocyst chimeras via injection of ES cells into blastocysts; (2) generation of ES-tetraploid or embryo-tetraploid chimeras through aggregation of diploid cells (ES or preimplantation 8-cell embryos) with tetraploid cells produced by electrofusion; (3) injection of DNA constructs into pronuclei of fertilized eggs to produce transgenic lines, and; (4) rederivation of mouse lines. At this time, ES-tetraploid and embryo-tetraploid chimeras have not been proposed. However, the Director and Staff have successfully produced such chimeras, and in the event they are needed. Core B will generate them. All equipment needed for technical services is presentiy functioning in Dr. Chaillet's laboratory at the Magee- Womens Research Institute. Because the services of the Core will be routinely used in all projects and reagents, equipment and mice will be shared and efficientiy used, significant savings in personnel and mousecosts are anticipated throuah the establishment of Core B.